I. Field of the Invention
The present invention relates to rotary position sensors.
II. Description of Related Art
There are many different situations in which the rotary position of a sensor must be determined. For example, most modern automotive vehicles include a throttle position sensor which detects the rotational position of the throttle plate and generates an electrical output signal representative of that position. That electrical signal is then electrically connected to an engine management unit which controls the overall operation of the internal combustion engine for the vehicle as a function of the position or depression of the throttle.
Typically, the previously known throttle position sensors include a rotatable body which attaches to the throttle plate shaft so that the body and throttle plate shaft rotate in unison with each other. Consequently, the rotatable position of the sensor is indicative of the rotational position of the throttle plate shaft and thus of the depression of the throttle.
In one type of previously known throttle position sensor, a transmitter coil is formed on a printed circuit board (PCB) and excited by a high frequency signal, e.g. 4 megahertz. A receiver coil is also formed on the PCB and is arranged in multiple segments around the PCB board wherein each segment is oppositely wound from the adjacent segments.
A coupler is then rotatably mounted relative to the PCB board so that the coupler is planar and overlies a portion of the PCB board. The coupler is constructed of an electrically conductive material so that rotation of the coupler relative to the PCB board varies the inductive coupling between the transmitting coil and receiving coil and thus varies the voltage output from the receiver coil. Consequently, the voltage output on the receiver coil is proportional to the relative rotational position of the coupler and, since the coupler is rotatably connected to the throttle shaft, of the rotational position of the throttle shaft and thus the depression of the throttle.
These previously known throttle position sensors, however, have more than two sets of receiving coils. Hence, they are more complex in construction. Furthermore, the resolvers have been bulky in construction.
A still further limitation of the previously known throttle position sensors is that it was difficult to achieve high accuracy in certain situations. For example, the output from the receiver coil may vary as a function of temperature which, in turn, creates an inaccuracy in the output signal from the receiver coil. Similarly, minor manufacturing tolerances, such as the position of the coupler relative to the PCB board and/or tilting of the coupler, also resulted in inaccurate output from the receiver coil.